Coronary heart disease is one of the most substantial threats to human life in the modern society. Hence, the importance of fast reliable non-invasive methods for the early detection of coronary heart disease may hardly be overestimated. One of the important parameters in the assessment of the physiological impact of coronary disease is the blood supply to various regions of the heart muscle. Reduced blood flow in the coronary capillary bed leads to insufficient blood supply and causes impairment of myocardial function. To date, there is no reliable method for the quantitative assessment of myocardial tissue blood flow, either invasive or non-invasive. Most of the techniques in current use provide information only on relative changes in regional myocardial blood flow, and none is sufficiently sensitive and accurate to supply a reliable absolute quantitative measurement in vivo. Moreover, the use of most of the known methods in humans is limited due to their invasive nature and high cost.
One of the recent developments promising to satisfy the clinical need for direct assessment of regional myocardial blood flow is associated with the use of contrast materials in ultrasonic imaging of the heart. A sonicated human Albumin solution was recently shown to be a nontoxic carrier of stable reproducible microscopic air bubbles comparable in size with the red blood cells (about 5 .mu.m in diameter), and therefore suitable for echocardiographic enhancement in humans. Using this material and other contrast enhancing solutions, the indirect qualitative assessment of myocardial tissue blood flow has been achieved. Visual examination of the differences in time dependence of the ultrasonic intensity reflected from various regions of the myocardium, following intracoronary or aortic root injection of the contrast solution, allowed the differentiation between underperfused and normally perfused myocardial tissue. Regions of myocardial tissue suffering from insufficient blood supply, are characterized by considerably lower contrast level and longer contrast clearance times, as compared with the normally supplied regions of the heart.
There have been several suggestions for providing quantitative markers related to regional blood flow, such as the time of peak contrast, the area under contrast appearance and washout curves, etc. However, insofar as we are aware, none provide a direct quantitative measurement of regional blood flow.